Israel must allow more aid into Gaza amid a blockade that is being used to "collectively punish more than two million people", a UN official has said.
A blockade on the territory has meant dwindling supplies of food, fuel, water and medicine, and both UN and Arab leaders have called for a ceasefire to allow for the entry of more humanitarian aid.
Philippe Lazzarini, the commissioner-general of the UN Palestinian Refugee Agency (UNWRA), said public services have collapsed and the region is on the brink of a serious outbreak of disease.
"On a daily basis, our colleagues have to prioritise now because they have to ration the very limited fuel that they still have," he told Sky News.
"Over the last few days, they had to decrease significantly the amount of fuel they provided to hospitals, to bakeries, to the water station. But in the coming days, if no more fuel is being made available to our colleagues, they will have to take even tougher decisions.
"And I have also warned that we are very close to almost a cessation of our operation because fuel is even needed for us to be able to move the trucks, to bring it in the warehouse, to distribute to the people being scattered in shelters."
Mr Lazzarini added: "I think we are on the brink of a serious outbreak of disease. It's not just a question of the water, but now we have also sewage water in the street.
"People have also their immunity being weakened, people start to be hungry, also the winter is also here, the rainy season is about to arrive and we have tens if not hundreds of thousands of people in the street. This disaster will become a real nightmare and a total catastrophe."
Earlier, he said: "The siege means that food, water and fuel, all basic commodities, are being used to collectively punish more than two million people."
Mr Lazzarini said negotiations have only resulted in a handful of trucks making their way into Gaza.
"This will not reverse the fact that Gaza is being strangled," he added.
Hospitals have found it difficult to source fuel to run emergency generators that power incubators and other life-saving equipment after Israel cut off all fuel deliveries to Gaza at the start of the war, forcing its only power plant to shut down.
Over the last week, Israel has allowed more than 80 trucks with aid to enter from Egypt through the Rafah crossing, the only entry point into Gaza not controlled by Israel.
But aid workers have said the convoys meet only a tiny fraction of the territory's rising humanitarian needs.
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Sheer scale of destruction
Some 7,300 Palestinians have died in the three weeks after Hamas staged a bloody attack into Israel, according to officials in Gaza.
On Thursday Gaza's Hamas-run health ministry said more than 3,000 minors and more than 1,500 women had been killed.
Footage from Sky News showed the scale of destruction caused by Israeli strikes on Gaza, as well as a boy being pulled from the wreckage of the aftermath of an attack.
Around 1.4 million of Gaza's 2.3 million residents have fled their homes, with nearly half crowding into UN shelters.
Hundreds of thousands remain in northern Gaza despite Israel ordering them to evacuate to the south and saying those who remain might be considered "accomplices" of Hamas.
More than 1,400 people were killed in the Hamas attack on Israel on 7 October, according to the Israeli government, with at least 229 hostages having been taken into Gaza.
Palestinian militants have fired thousands of rockets into Israel, including one that hit a residential building in Tel Aviv on Friday and injured four people.
An Israeli ground attack on Gaza is expected to cause even higher casualties on both sides as they battle each other in dense residential areas.